1. Field of the Invention
The present invention relates to a display device with integrated touch screen and a method of driving the same, which reduce a touch error due to the switch of a screen and thus enhance touch sensing performance.
2. Discussion of the Related Art
With the advancement of various portable electronic devices such as mobile terminals and notebook computers, the demand for flat panel display devices applied to the portable electronic devices is increasing.
Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, organic light emitting diode (OLED) display devices, and electrophoretic display (EPD) devices have been developed as flat panel display devices.
The application fields of flat panel display devices are being expanded because the flat panel display devices are easily manufactured and have drivability of drivers, low power consumption, high image quality and a large screen. Instead of input devices such as conventionally applied mouses or keyboards, a touch screen that enables a user to directly input information with a finger or a pen is applied as an input device for flat panel display devices.
A touch screen is applied to monitors such as navigations, industrial terminals, notebook computers, financial automation equipment, and game machines, portable terminals such as portable phones, MP3 players, PDAs, PMPs, PSPs, portable game machines, DMB receivers, and tablet personal computers (PCs), and home appliances such as refrigerators, microwave ovens, and washing machines. Especially, since all users can easily manipulate the touch screen, the application of the touch screen is being expanded.
Touch screens are divided into resistive touch screens, capacitive touch screens, and infrared touch screens according to a sensing type. The capacitive touch screens have convenience in manufacturing and excellent sensing performance, and thus are widely applied.
Moreover, the type of a touch screen is divided into an in-cell type in which a touch screen is built in a cell of a display panel, an on-cell type in which a touch screen is disposed on a display panel, and an add-on type in which a touch screen is separately coupled to an upper portion of a display device, according to a structure. The in-cell type touch screen has aesthetic design and is slimmed, and thus is recently applied.
FIG. 1 is a diagram schematically illustrating a related art display device including a touch screen. FIG. 2 is a diagram showing problems which are caused by an auto touch error due to the switch of a screen.
Referring to FIG. 1, the related art display device including a touch screen includes a display panel 10, a driver integrated circuit (IC) 20, and a touch IC 30.
In the display panel 10, a plurality of pixels are formed, and a certain number of pixels (for example, 64×64 pixels) configure a touch group (touch block TB) 12 to form a touch screen. In this case, a common electrode supplying a common voltage Vcom is formed in each of a plurality of pixels that configure each of a plurality of the touch groups 12. The respective common electrodes of each touch group 12 are connected to the touch IC 30 through separate touch lines (not shown), and, by driving the common electrodes as touch electrodes, the touch screen senses a user's touch.
In an in-cell touch type, due to a structural feature in which both pixels for display and a touch screen for touch detection are formed, display and touch sensing are temporally divided and driven. A capacitance is changed in a corresponding touch block 12 which is touched by a user's finger during a touch sensing period (non-display period), and the touch IC 30 senses the capacitive change in each touch block 12, thereby sensing whether there is a user's touch and a touched position.
Referring to FIG. 2, when a display period is completed (a gate-off state), a plurality of pixel electrodes formed in the display panel 10 are floated. However, due to an overlap capacitance and coupling between a gate and a pixel, the pixel electrodes are not completely floated, and thus, a capacitance is generated between a corresponding common electrode and a corresponding pixel electrode.
A capacitance, generated between a common electrode and a pixel electrode, is divided into a storage capacitance (Cst) and a liquid crystal capacitance (Clc) generated with a fringe field. In this case, the liquid crystal capacitance is changed by the switch of a screen, and thus, an initial capacitance is greatly changed. For this reason, a malfunction occurs in touch sensing.
When a display screen is switched, for example, when the display screen is switched from a black screen to a white screen or switched from the white screen to the black screen, the capacitance of a liquid crystal layer is changed, and thus, the initial capacitance is changed. For example, when the display screen is switched from full black to full white, the amount of changed touch raw data becomes 150 to 200 averagely.
The initial capacitance of each pixel is severely changed by the switch of a screen, in which case a capacitance is changed greater than the capacitive change due to a user's finer touch. For this reason, whenever the luminance of a screen is greatly changed, the capacitance of the liquid crystal layer is changed, causing a touch error.
When the amount of changed touch raw data in the touch block 12 exceeds 120, the touch IC 30 determines there to be a user's touch. That is, an auto touch error is caused in which the touch IC 300 determines there to be a touch even when a touch is not actually performed, and thus, when a screen is switched, a severe error which degrades the reliability of touch sensing occurs.
Furthermore, the amount “Δ data” of changed touch raw data for each image luminance generally shows a trend similar to a gamma curve of 2.2, and, the amount of changed touch raw data due to the switch of a screen increases in proportion to the increase in touch sensitivity. For this reason, there is a limitation in enhancing touch sensing performance.
Moreover, in the related art display device including the touch screen, since it is impossible to perform an action and a rework for solving a defect (which is caused by the manufacturing deviation of the display panel) after the manufacturing of the display panel is finished, it is difficult to reduce a touch error due to the switch of a screen.